Breathing devices for diving can be broadly divided into two types, one type being an open-type breathing device and the other type a closed-type or semi-closed type breathing device. In an open-type breathing device, gas that has been breathed once is expelled from the device, but a closed-type or semi-closed type breathing device includes an apparatus that enables gas that has been breathed to be used again.
A closed-type or semi-closed type breathing device generally has the advantage of being lighter than an open-type breathing device and permitting longer dives to deeper depths. However, since conventional closed-type or semi-closed type breathing devices were developed for specialized diving applications or military use, they were equipped with only a minimum of safety mechanisms, and has no mechanisms for coping with emergency situations that occur relatively easily. For this reason, rigorous training was required to use this type of device, and thus it could not be readily used by recreational divers.
However, the growing popularity of diving generated increasing demand for closed-type or semi-closed type breathing devices that were not overly complicated to operate and did not require such rigorous training.
Equipped as it is with oxygen concentration sensors and the like, a closed-type breathing device requires considerable training with respect to handling, control and monitoring. In contrast, a semi-closed type breathing device has no such equipment and therefore can be operated without training, so it can be handled relatively easily even by a non-expert.
Semi-closed breathing devices that are simpler and easier to use than before would be highly convenient. There are various improvements that can be implemented to make such semi-closed type breathing devices more readily accessible than before.
For example, since the pressure in the mouth piece and in inhalation and exhalation passages in communication with the mouth piece is about the same as the surrounding pressure, outside water can enter the device via the mouth piece.
If a person using the device is novice, there is quite a high possibility that while submerged the mouth piece may become dislodged from the person's mouth, allowing water to enter the device through the mouth piece. This water can have an adverse effect, such as on the carbon dioxide gas adsorption device. Thus, a mechanism that does not allow the intrusion of water into the device is desirable, and there is a need for a mechanism that will automatically expel any water that does enter.
In the case of an inhalation passage, this type of problem can be resolved by the provision of a check valve at the connection between the inhalation air hose and mouth piece that only permits a fluid to pass from the inhalation air hose to the mouth piece. However, a check valve does not solve the problem in the case of exhalation passage, since exhaled air has to be passed from the mouth piece to the exhalation air hose, so a different contrivance is required.
In contrast, because an open-type breathing device does not have an exhalation air hose and the pressure inside the inhalation air hose is higher than the surrounding pressure, the entry of outside water into the device via the mouth piece does not occur.
Concerning this point, in International Patent Publicly Disclosure No. WO 95/09762 the applicant of this patent application proposed a mouth piece unit that is easy to use, even by a novice. This mouth piece unit has a manually operated assembly, operation of which caused chewing pieces to project out from the mouth piece, and the diver continues to be supplied with fresh breathing gas as long as the chewing pieces are held in the mouth. If the diver should accidentally let the mouth piece come out of his or her mouth, the chewing pieces retract into the mouth piece unit, closing off the exhalation air hose. Thus, the result is that the entry of water is prevented automatically.
In addition to the manually operated assembly, a purge lever is provided that when operated causes fresh breathing gas to be delivered at a high flow rate to purge the mouth piece unit of water. Thus, a diver can expel any water in the mouth piece unit simply by operating this purge lever.